1. Field of the Invention
The present invention relates to a projection apparatus for projecting a pattern image to an object so as to detect the focus state of a phototaking system or observation system and a phototaking apparatus using the same, and particularly, the invention is preferable to an apparatus for detecting, by a phase difference scheme, the focus state of a phototaking system or observation system on the basis of the reflected light-received image of a pattern image projected to an object.
2. Related Background Art
If the luminance or contrast of an object is low, some apparatuses for optical devices such as cameras, cinecameras, and video cameras using the TTL scheme illuminate the object with an illumination (projecting) unit incorporated in the camera body or strobe unit, or project onto the object the image of a projecting pattern which has a predetermined pattern and is incorporated in the illumination unit together with a projecting lens, thereby giving contrast for focus detection.
FIG. 12 is a view showing the arrangement of a projecting system in a projection apparatus of a type which projects a pattern image onto an object. Referring to FIG. 12, a light source 104 is formed from, e.g., an LED. A projecting pattern (mask) 103 has light-shielding portions 103a and light-transmitting portions 103b formed from, e.g., a plurality of linear strips, as shown in FIG. 13. The projecting system also has a projecting lens 102.
Referring to FIG. 12, the object side is irradiated through the projecting lens 102 with, of light components from the light source 104, a light component transmitted through the light-transmitting portions 103b. A pattern image corresponding to the projecting pattern 103 is projected onto the object. The reflected image of the pattern image is received and detected by a focus detection system (not shown) of phase difference scheme, thereby detecting the focus state of the phototaking system.
FIG. 14 is a view showing the irradiation (illumination) range of projected light and the projected pattern image on the object. Referring to FIG. 14, a dotted line 121 indicates the illumination range, and hatched portions 122 indicate the pattern image.
In such a projection apparatus, the focus detection range of a phototaking apparatus on which the projection apparatus is installed is often located at the center of the phototaking frame (the optical axis center of the phototaking lens), and only the center of the object side is illuminated with the projected light except for parallax correction.
In recent years, a camera for detecting focus states at a plurality of points on an object has been proposed. In this case as well, the above-described scheme of projecting a pattern image with a predetermined pattern to the object side and detecting a reflected pattern image from the object to execute focus detection is effectively used. In another proposed scheme, instead of laying out a focus detection region only in one of the horizontal and vertical directions in the phototaking frame, focus detection regions are laid out in both the horizontal and vertical directions such that the focus detection regions in the two directions cross at the central portion of the frame. This apparatus aims at obtaining a satisfactory focus detection result without any limitation on the contrast direction of the object.
In such a projection apparatus used for a phototaking apparatus having a plurality of focus detection regions or focus detection regions laid out in two directions perpendicular to each other, it is difficult to simultaneously project a pattern image to the plurality of focus detection regions using a projecting system of conventional scheme.
To simultaneously project a pattern image to a plurality of points, a large pattern image must be prepared in advance and formed in a wide range. Alternatively, a pattern image with a very fine pattern must be formed in a wide range using a projecting lens having a wide view angle and a very short focal length.
In either case, to form a satisfactory pattern image on an object, the aberration of the projecting lens must be satisfactorily corrected throughout a wide view angle. It is considerably difficult to realize it with a compact arrangement. In addition, in the above-described scheme of preparing a large pattern image, the light source for illuminating the large pattern image must be made large, and no compact arrangement can be obtained.
Furthermore, in the above-described scheme of forming a pattern image using a projecting lens with a very short focal length, the aperture of the projecting lens can hardly be made large, and therefore, the reach of illumination light cannot be made sufficiently long. It is also hard to prepare a very fine pattern image.
To solve these problems, Japanese Patent Application Laid-Open No. 63-47710 proposes an apparatus which implements the above-described scheme of preparing a large pattern image using a plurality of illumination light sources. However, this arrangement cannot solve the above-described problem of projecting lens aberration correction.
Considering this point, the present assignee has proposed, in Japanese Patent Application Laid-Open No. 2-101413, a projection system for focus detection which uses, as a projecting lens for projecting a pattern image, a plurality of lenses having an aperture shape long in the longitudinal direction of the stripes of the pattern image and short in the vertical direction of the stripes.
Along with the demand for a large focus detection region of the phototaking apparatus, the pattern image projecting range of the projection apparatus must also become large. In addition, a pattern image projecting scheme that is effective when focus detection regions in the two directions cross at the central portion of the phototaking frame has not been proposed yet.